Conventionally, an electric contact, such as a connector, is made of copper or copper alloy electrode. The electrode is plated with nickel, and then an outermost surface of the electrode is plated with tin.
When a temperature of usage environment changes, an electronic device and the like having an electric connection at an electric contact repeats expansion and contraction based on a thermal expansion coefficient of material used for the device. Accordingly, a repeated micro sliding of the electric contact occurs.
Due to the repeated micro sliding, the electric contact may be worn away, and oxidation of tin covering the electric contact may proceed at a contact portion. Accordingly, a contact resistance may increase, and the electronic device and the like may malfunction.
FIG. 1 is a diagram shoving an electric contact film according to a related art. When electric contact films 11a, 11b are worn away due to a repeated micro sliding, an oxide 12 is formed at an interface. Accordingly, resistances of the electric contact films 11a, 11b increase, and thereby the electronic device and the like malfunctions.
In order to solve the above-described issue, an outermost surface of an electrode may be plated with gold after plated with nickel. When the outermost surface of the electrode is covered with gold, oxidation does not progress even if a sliding occurs. Thus, the contact resistance does not increase due to oxidation.
However, under circumstances in which a micro sliding occurs for a long time, a gold plating film may be worn away due to the micro sliding. If the gold plating film on the surface of the electric contact is fully worn away, a nickel plating film under gold is exposed, and oxidation of nickel progresses due to the micro sliding. As a result, the contact resistance increases. Therefore, in order to secure a sufficient sliding life, it needs to increase a thickness of the gold plating film, and a cost increases.
JP-A-54-69531, JP-A-6-330392, JP-A-2008-248294 disclose films in which lubricant-filled microcapsules are dispersed in metal matrix using a composite plating method as examples of electric contacts for increasing a sliding life without a thick gold plating film.
In the films, the minimum dispersion size of the microcapsules is about 3 μm, and a lubricant starts to function after wear progresses to an extent. Thus, an effect of restricting wear is not sufficient. In addition, because the films do not have a function of restricting oxidation of a surface of an electric contact, an oxide film may be formed at the electric contact, and the contact resistance may increase.
Japanese Patent No. 4,176,081 discloses an electrode in which a depressed portion is provided on a plating surface, and then the plating surface is impregnated with fluorine compound. Also in this electrode, there is the above-described issue.